Pool Volume Calculator (USA)
Estimate how many gallons of water your swimming pool holds by shape and depth, see the volume in liters and cubic meters, estimate fill cost and fill time, and download a professional PDF report.
| Avg Depth | Gallons | Liters | Water Weight | Fill Time |
|---|---|---|---|---|
| Calculate to see scenarios | ||||
The highlighted row is your pool at its current average depth. Scenarios show how volume, weight and fill time change if the average depth is different.
How to Use the Pool Volume Calculator
Find out how many gallons of water your pool holds — plus liters, cubic meters, water weight, fill cost and fill time — in four steps.
Pick your pool shape
Rectangle, round, oval or kidney. The formula badge under the shapes updates as you switch, so you can always see exactly how the number is being worked out.
Enter the dimensions
Type the measurements in feet or drag the sliders. Rectangles and ovals take length and width, round pools take a diameter, kidney shapes take a length plus a wide and narrow width.
Set the water depth
Choose constant depth for an above-ground or flat-bottom pool, or shallow-to-deep for a sloped floor. Enter both ends and the average depth is calculated for you.
Add water price and hose rate
Put in your cost per 1,000 gallons and your fill rate in GPM to get an estimated fill cost and fill time — then download the two-page PDF report.
What’s Included
One gallon number is where every chemical dose, pump size and water bill starts — this works it out four ways and shows what it costs to fill.
Four pool shapes
Rectangle, round, oval and kidney, each with its own geometry — including the standard freeform approximation for kidney-shaped pools rather than treating them as a box.
Constant or sloped depth
Enter one uniform depth, or a shallow end and a deep end and let the average be worked out. The average depth is shown as you type, because that’s the number the volume rides on.
Gallons, liters, m³ and ft³
The same pool in US gallons for chemicals, liters and cubic meters for metric equipment specs, and cubic feet for the raw geometry — plus surface area and total water weight.
Fill cost and fill time
Enter your water rate per 1,000 gallons and your hose or truck fill rate in GPM to see what the fill costs and how long it takes — in hours or days, whichever makes sense.
Charts and depth scenarios
See your pool against small, average and large pools, how the volume splits between the shallow and deep halves, and a table of what every average depth from 3 to 7 feet would hold.
Branded PDF report
Two pages with your pool details, full volume breakdown, water weight, fill cost and time, a comparison bar chart and the depth scenario table — handy for a pool pro or a builder.
By the Numbers
A quick snapshot of the constants and conversions working behind the calculator.
rectangle to kidney
in one cubic foot
per gallon
typical fill rate
no sign-up needed
Built for “How Many Gallons Is My Pool?”
Chemical doses, pump sizing, heater run time and your water bill all start from the same number — and almost nobody has it written down.
Owners dosing chemicals
Every label on the shelf is written per 10,000 gallons. Get the real volume once, write it on the equipment pad, and stop guessing at chlorine, shock and stabilizer.
Anyone filling or refilling
New build, liner swap or a spring refill after a drain-down — see what the water will cost at your utility’s rate and how many hours or days the hose will actually run.
Equipment shoppers
Pumps, filters, heaters and salt systems are all rated by volume. Know your gallons before you shop and you can check turnover and BTU sizing instead of taking a rep’s word.
Measure the Water, Not the Pool
Seven things that separate a volume figure you can dose chemicals against from one that’s off by thousands of gallons.
- 1Use water depth, not wall height. The waterline usually sits several inches below the coping or the top rail, roughly halfway up the skimmer opening. Measuring the wall instead of the water can add thousands of gallons to a full-size pool — measure down from the actual surface.
- 2Average depth only works on a straight slope. Adding the shallow and deep ends and halving them assumes the floor drops evenly the whole way. Most in-ground pools have a long flat shallow section, then a short slope into a deep hopper — that shape holds less than the simple average suggests.
- 3Split a complex pool into sections. For an L-shape, a Roman end or a pool with a flat shallow area and a separate hopper, calculate each section on its own and add the gallons together. It takes two minutes and beats a single rough guess by a wide margin.
- 4Treat the freeform result as an estimate. Kidney and lagoon shapes use an area factor, not exact geometry, so expect a reasonable ballpark rather than a precise figure. If you want it tighter, measure the widest and narrowest spans and break the pool into rectangles.
- 5Round down when you dose, not up. If your volume is an estimate, using the lower end keeps you from overshooting on chlorine or stabilizer. Under-treating is a retest and another scoop; over-treating cyanuric acid in particular can only be fixed by draining water.
- 6Ask about a sewer credit before you fill. Many utilities bill sewer charges based on water use, so filling a pool can cost you twice. Some offer a pool-fill credit or a second meter, and bulk water delivery is occasionally cheaper — worth one call before you open the tap.
- 7Check the fill time before you start. A typical garden hose moves roughly 9 gallons a minute, which turns an average pool into a day and a half of continuous running. Fresh plaster usually has to be filled without stopping, and a well or a soft-water system may not keep up — plan the source, not just the schedule.
Frequently Asked Questions
Answers to the most common questions about pool gallons, average depth, fill cost and fill time.
How many gallons is my swimming pool?
Work out the water surface area in square feet, multiply by the average water depth in feet to get cubic feet, then multiply by 7.48 to convert to US gallons. A rectangle is length times width; a round pool is 3.14 times the radius squared; an oval is roughly 0.785 times length times width; a kidney uses about 0.45 times the two widths added together times the length. So a 16 by 32 foot rectangle with a 5.5-foot average depth holds about 21,000 gallons. The calculator applies the right formula for whichever shape you select.
How do I find the average depth of a pool?
For a floor that slopes evenly from one end to the other, add the shallow depth and the deep depth and divide by two — a 3-foot shallow end and an 8-foot deep end averages 5.5 feet. That shortcut breaks down on the more common layout of a long flat shallow section followed by a short slope into a deep hopper, which holds noticeably less water than the simple average implies. For those pools, measure the flat shallow area and the deep section as separate volumes and add them together. Above-ground and flat-bottomed pools have a constant depth, so no averaging is needed at all.
How much does it cost to fill a swimming pool with water?
Municipal water commonly runs a few dollars per 1,000 gallons, so a 20,000-gallon pool often lands somewhere in the tens of dollars for the water itself — but rates vary enormously between utilities and tiered pricing can push the cost up as usage climbs. The bigger surprise is usually the sewer charge, since many utilities bill sewer as a share of metered water even though pool water never reaches the sewer. Ask whether a pool-fill credit or a separate irrigation meter is available before you fill. Enter your own rate per 1,000 gallons in the calculator and you’ll get an estimate based on what you actually pay rather than a national average.
How long does it take to fill a pool with a garden hose?
Divide the gallons by your fill rate in gallons per minute. A standard garden hose delivers roughly 9 GPM, so 20,000 gallons takes about 2,200 minutes — close to 37 hours, or a day and a half of continuous running. Two hoses roughly halve it, and water delivery by truck is far faster if you’re on a well or in a hurry. Your actual rate depends on hose diameter, length and house pressure; time a five-gallon bucket to measure it, then enter that number for a realistic estimate.
How much does the water in a pool weigh?
Fresh water weighs about 8.34 pounds per US gallon, so multiply your gallons by 8.34. A 20,000-gallon pool holds roughly 166,800 pounds of water — over 80 tons. That figure matters most for above-ground pools and any pool on a deck, rooftop or sloped lot, where the ground or structure underneath has to carry the load. It’s also why a full pool should never be drained casually: the water pressure inside is part of what holds the shell and the surrounding soil in balance.
Why does the exact volume matter for pool chemicals?
Every dosing instruction on a bucket of shock, a bottle of algaecide or a bag of stabilizer is written per volume of water, usually per 10,000 gallons. If your working number is off by a few thousand gallons, every dose you’ve ever made has been off by the same proportion — which is a common reason chlorine never quite holds or a reading refuses to move. Overshooting matters more than undershooting with some products: excess cyanuric acid, for example, can generally only be reduced by draining and replacing water. Calculate the volume once, write it somewhere near the equipment, and dose from that.